1. Field of the Invention
This invention relates to emulsion-type adhesive compositions which includes a copolymer of isoprene and sulfopropyl-N-methacroyloxyethyl-N,N-dimethyl ammonium-betaine, wherein the sulfobetaine copolymer has about 0.15 to about 15.0 mole % of sulfobetaine groups, and less than about 300 parts by weight of a hydrocarbon resin of a petroleum or coal tar distillate, having about 5 to 6 carbon atoms, the hydrocarbon resin being composed of aliphatic dienes and mono-olefins per 100 parts by weight of the sulfobetaine copolymer.
Broadly speaking, synthetic adhesives used in packaging can be classified into four categories: water-based emulsion system, solvent-based, reactive and hot melt adhesives. Of these four, currently the water-based are used most extensively. Usually the water based adhesives are based on emulsion polymers and are applied to porous cellulosic substrates. Energy from the outside in some fashion is applied to the system to evaporate the water in order that a strong bond may be formed.
With the solvent-based adhesives, usually a good wetting is achieved; however, their use has been becoming extremely restrictive due to expensive energy requirements for the evaporation of organic solvents, fire hazards associated with the use of these organic solvents and emissions problems with said solvents. The strict governmental regulations and restrictions concerning workers' exposure to solvent vapors, etc. has placed extra pressure on the packager to use non-solvent-based adhesives.
The hot melt adhesives are generally applied (as the name implies) by conventional extrusion or coating techniques in the temperature range of 250.degree. to 450.degree. C. on one of the surfaces to be bonded. The other surface is brought in contact with the hot surface for a sufficient period of time for the melt to cook, where, upon solidification, a strong and durable bond is formed.
As a result of various local and federal safety and environmental regulations, the polymers adhesive industry is moving from solvent- to water-based technology. Usually the water-based pressure-sensitive adhesives are based on emulsion polymers and applied to porous cellulosic substrates. Energy is applied to the system to evaporate the water in order to form a strong bond. The key requirement of such an emulsion is that it forms a uniform coating having good adhesive (tack) and cohesive characteristics. The degree of the adhesive and cohesive strength of the final adhesive product is established by its end use. For example, for general label applications, it is desired that the product have aggressive tack and not so much cohesive strength. However, for general tape uses, the composition should have good cohesive strength with marginal tack properties.
Currently in the market, there are very limited emulsion polymers available for water-based adhesives. A few acrylic polymer emulsions are available which are suitable for label applications, but these are relatively expensive. There is not a single water-based polymeric adhesive available in the market which meets the requirements for tape applications, especially the tapes desired by the automotive painting industry.
2. Prior Art
Several U.S. patents have described sulfonated polymers such as sulfonated butyl and sulfonated EPDM in adhesive applications (e.g., U.S. Pat. No. 3,867,247 and U.S. Pat. No. 3,801,531). It is important to distinguish the instant invention over those prior art systems. The former patents are directed at a sulfonated butyl cement or EPDM terpolymer which is solvent based and is employed to laminate various substrates. It is important to note that the instant invention differs dramatically from these patents as follows:
(a) The adhesives of the instant invention are not deposited from solvents, but are water-based emulsions; PA1 (b) The instant invention may optionally include either a tackifier resin and/or plasticizer capable of associating with the neutralized sulfonate groups. PA1 (c) The instant invention is directed to sulfobetaine elastomeric copolymers, whereas most of the prior art deals with sulfonated butyl rubber (e.g., U.S. Pat. No. 3,867,247).
There are a limited number of water based (emulsion) polymers which have reportedly given good adhesive and strength properties when mixed with appropriate resins. One class is the acrylics but these suffer the aforementioned disadvantages. Another example is a copolymer of isoprene and sodium styrene sulfonate (ISS) Agarwal et al. U.S. Pat. No. 4,387,174. However, the latter polymers can experience difficulties with emulsion stability and/or solids level, incorporation of sulfonate groups and (when mixed with appropriate resins) irreproducible of property profiles.